1) Field of the Invention
The present invention relates to novel fluoran compounds which are useful as chromogenic compounds in recording materials such as pressure sensitive and heat-sensitive recording materials. More particularly, the invention relates to crystal of a fluoran compounds in crystalline form, to crystalline toluene adducts thereof, to a process for the preparation of these compounds and to recording materials comprising these compounds.
2) Description of the Prior Art
Pressure-sensitive recording, heat-sensitive recording and electroheat-sensitive recording have conventionally been used as systems for recording transfered information through the mediation of external energy, such as pressure, heat or electricity, by utilizing a color reaction between a colorless or pale colored electron donative compound (chromogenic compound) and an organic or inorganic electron acceptor (developer).
In these systems, fluoran compounds have widely been used as the chromogenic compound.
Many fluoran compounds are known in the prior art, including those having structures similar to the fluoran compounds of the invention, for example, those having the formulas (A), (B), (C), (D) and (E). ##STR2## Japanese Patent Laid-Open Publication SHO 48-43296(1973) ##STR3## Japanese Patent Laid-Open Publication SHO 48-43296(1973) Japanese Patent Laid-Open Publication SHO 60-202155(1985) ##STR4## Japanese Patent Laid-Open Publication SHO 48-23204(1973) ##STR5## Japanese Patent Laid-Open Publication SHO 54-34909(1979) ##STR6## Japanese Patent Laid-Open Publication SHO 59-197463(1984)
However, the compound of the formula (A) has the disadvantage of very low solubility in capsule oil when the compound is used in a pressure-sensitive recording material. Additionally, in the case of applying to the heat-sensitive recording material, the compound has the defect that the compound itself colors gray to dark gray when mixed with a developer such as bisphenol A and provide only a gray to dark gray colored (soiled) paper by applying the mixture to a paper.
The chromogenic temperatures of the compounds of formulas (B), (C), (D) and (E) are too high to permit their use in a heat-sensitive recording material. Consequently, the performance of these prior art compounds cannot fully meet the present market demand for more rapid and higher density recording. Therefore, a chromogenic compound capable of quickly developing color at a lower temperature has been strongly desired.
Further, the compounds of formulas (A)-(E) are poorly soluble in capsule oil and their performance is still unsatisfactory for the pressure-sensitive recording material.